The present invention relates generally to power distribution components, and more particularly, to automatic power restoration systems and methods for use in power distribution systems.
The basic functions of a power system are to continuously maintain an adequate and reliable supply of electric power to customers. However, performing these functions is not always possible because various types of failures occur randomly and beyond the control of system engineers. Power system planners, designers, and operators are generally concerned with the reliability of their systems and the determination of realistic availability targets for their systems. Recently, this concern has been accentuated by the introduction of competition in the marketplace among utility companies. Now, utility companies are jockeying among themselves to provide distinguishable services in an effort to sustain existing customers and to attract new customers.
Residential customers and businesses alike are increasingly depending on power. From a simple toaster to complex manufacturing equipment, power is required by today""s power customer in most of their day to day operations. Not surprisingly, as a result of the new competition and the importance of power to customers, power system operators are being asked to provide reliable, dependable, and more affordable power. Power system operators have taken notice since the consequences of long-term unavailability and persistent interruption of electric power could directly translate to a loss of power customers.
As a result, power system operators are constantly developing improved components for power distribution systems that will enhance the system""s reliability. For example, many power utilities around the world use fuses on their lateral lines. In addition to fuses, utilities may employ an automatic power restoration device such as a circuit recloser or reclosing breaker. These devices generally operate by sensing overcurrents, time and interrupt currents, and reenergize a distribution line by reclosing automatically. If a fault in the power distribution system is permanent, the recloser locks open after a pre-set number of operations (usually three or four), isolating the faulted section from the main part of the systems. A recloser control device provides the intelligence that enables a recloser to sense overcurrents, select timing operations, time the tripping and reclosing functions, and lockout. The hydraulic control, an integral part of the recloser, is used in single-phase reclosers and the smaller rated three-phase reclosers. The electronic control is generally used in the single-phase reclosers and in higher rated three-phase reclosers. Such devices, however, should be appropriately programmed to coordinate in a predefined manner to ensure that the power distribution systems respond to line faults in accordance with expectations.
Generally, when reclosers are used in conjunction with fuses, they are configured in a variety of modes. For example, the recloser or reclosing breaker may be configured for a Fuse Saving mode or Fuse Clearing mode. In the Fuse Saving mode, the automatic circuit recloser or reclosing breaker operates a couple of operations faster than a fuse, trying to clear a momentary fault. If the fault is still present, the automatic circuit recloser operates more slowly than the fuse, enabling the fuse to clear. In the Fuse Clearing mode, the automatic circuit recloser is setup so that for a fault beyond any fuse in series with the recloser, it shall be cleared by the fuse without causing the recloser to close.
In operation, reclosers or reclosing breakers typically employ two curves for protection: an ANSI 50 and an ANSI 51 protection curve. These curves are typically referred to as slow and fast curves, respectively. Depending on the utility practice, these curves are coordinated with other protection devices, such as a fuse on the circuit. However, it is not always possible to properly coordinate the fuse curve and the recloser curve over the entire current range. Due to coordination limitations, there are frequent times when it is possible for a fault to occur that has sufficient magnitude to cause the fuse to melt (i.e., irreversible damage to the fuse), but not to clear the fault before the upstream protection (e.g., recloser) will respond.
It would thus be advantageous to develop apparatus and methods for providing automated restoration of power distribution systems that do not place the power restoration components at risk during a fault.
The present invention is directed to apparatus and methods for providing an automatic power restoration device with a programmable or modifiable end point. The end point is indicative of the operational parameters of the automatic power restoration device. A user can modify the end point and thus the operational parameters of automatic power restoration device.
In one embodiment of the present invention, the end point is determined according to the protection characteristics of other fault protection devices within a power system. This configuration prevents the automatic power restoration device from unnecessarily operating when another fault protection has previously isolated a fault. Such unnecessary operations of the automatic power restoration device cause excessive wear and tear to the automatic power restoration device as well resulting in unwanted operation.